1. Field of the Invention
The present invention relates to a light apparatus of an optical mouse and the light projection method. In particular, this invention provides a light apparatus of an optical mouse with an aperture stop and the light projection method thereof.
2. Description of the Related Art
An optical mouse detects the image on the image detection surface by using an image detection unit and moves the cursor displayed on a display unit. The sensitivity of the movement of the cursor depends on whether the image detection unit detects clearly the image on the image detection surface or not.
Reference is made to FIG. 1. The optical mouse of the prior art comprises a light apparatus 1, a light source 2 and an image detection unit 3. The light apparatus comprises a light-guiding body 10 and an image-forming lens 11. When an optical mouse is moved on an image detection surface 5, the light of the light source is projected onto the image detection surface 5. The light is reflected from the image detection surface 5 and passes through the image-forming lens 11 to the image detection unit 3. In this way, the image detection unit 3 detects the image on the image detection surface 5. The image detected from the image detection unit 3 is calculated and processed by a circuit unit (not showed on the figure) to judge the direction and the displacement of the optical mouse's movement and move the cursor on a display unit.
When the light of the light source 2 passes through the image-forming lens 11, the light apparatus 1 of the optical mouse of the prior art produces a light halo (also called haze) on the image detection unit 3 of the optical mouse due to aberration, as shown in FIG. 2. The two ends of the image detected on the image detection unit 3 are curved and vague, due to the curvature of the image-forming lens 11. As a result, the image detection unit 3 can't clearly detect the image of the image detection surface 5. Therefore, the cursor on the display unit can't be moved sensitively.
If an aperture stop 15 is made integrally in one piece with an image detection unit 3, the cursor on the display unit can be moved sensitively, as illustrated in FIG. 1A. However, the above image detection unit 3 only operates with an image-forming lens 11 having a sole type of curvature to enhance the detection effect. When the curvature of the image-forming lens 11 is different, the distance between the image detection unit 3 and the image-forming lens 11 needs to be changed and the dimension and the installation position of the aperture stop 15 also need to be changed in order to have a good detection effect. This will increase the manufacturing cost of the optical mouse.